In a certain code language, each letter is assigned a unique digit. Based on the following codes: PLANE is coded as 74851 and DOG as 392, how is GOLD coded?
- (a)2843
- (b)2943
- (c)2394
- (d)2934
Answer
Why
Correct — B.
Rule: each letter keeps one digit, matched by position.
PLANE = 74851: P = 7, L = 4, A = 8, N = 5, E = 1.
DOG = 392: D = 3, O = 9, G = 2.
GOLD: G = 2, O = 9, L = 4, D = 3
→ 2943, option (b).
Why the others are wrong
- (a)2843 — 2843 puts 8 in second place, but 8 is the code for A, the third letter of PLANE. O comes from DOG, where it is 9.
- (c)2394 — 2394 uses the right four digits in the wrong order. Read back, 2-3-9-4 spells G, D, O, L, not GOLD.
- (d)2934 — 2934 swaps the last two digits. L is 4 and D is 3, so GOLD must end 4-3, not 3-4.
Concept
In a letter-to-digit code each letter stands for one fixed digit. When a word is coded letter by letter, the digit in each position belongs to the letter in that position.
Write the key out as a table first, then build the target word from it. Every letter of GOLD appears in PLANE or DOG, so nothing has to be guessed.
PLANE and DOG share no letter and no digit, so each digit is read straight off its position. When two coded words do share letters and the digits are jumbled, the method changes: match the common letters to the common digits.
Key facts
- PLANE → 74851 gives P = 7, L = 4, A = 8, N = 5, E = 1.
- DOG → 392 gives D = 3, O = 9, G = 2.
- GOLD takes G, O and D from DOG and L from PLANE: 2-9-4-3.
Study next
Common traps
- Taking O's digit from the third place of PLANE (8, which is A) instead of from DOG
- Writing the right four digits in the wrong order, as in 2934 or 2394
12 Sep 2025, 12:30, Reasoning Q.19 sets the same kind of code: MOUSE is 45291 and RAT is 786, and STORE is keyed 96571.
17 Sep 2024, 12:30, Reasoning Q.8 jumbles the digits instead: TIDE is 9457 and DENT is 7593, and N is keyed 3, the digit DENT does not share with TIDE.
Related PYQs
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